Electronic apparatus at the potential of a high-tension electric line must still receive power even when no tension is applied to the line. Two known ways of doing this consist, either in using a battery and a charger kept at the potential of the electric line in which case it is necessary to de-energize the line for maintenance or else in supplying power via an isolating transformer (in which case an isolating transformer of considerable dimensions is required to transmit even a few watts of power, once the line is one which operates at several kilovolts).
Preferred embodiments of the present invention avoid these drawbacks while allowing the electronic apparatus to be powered independently from the presence or absence of the electric potential. Such embodiments also provide a supply circuit which is simple to put into use, in particular when equipped with a capacitor voltage transformer which is also used to monitor the high potential.